This invention relates to a switched capacitor filter.
An example of a prior art switched capacitor filter is shown in FIG. 14. This filter is a one-stage low-pass filter including switched capacitor circuits 1 and 2 and an integrator 3. The switched capacitor circuits 1 and 2 perform a function of a resistance element and the switched capacitor circuit 1 is constructed of a capacitor 10 and four analog switches 11 to 14. The other switched capacitor circuit 2 is of a similar construction.
In this filter, the analog switches 11 and 13 are brought into conduction by a clock .PHI.a which is generated at a predetermined interval. By conduction of these analog switches 11 and 13, a signal path from the analog switch 11 to the ground through a capacitor 10 and the analog switch 13 is formed. By supplying an input signal through this signal path, an electric charge corresponding to the level of the input signal is held in the capacitor 10. The analog switches 12 and 14 are brought into conduction by a clock b which is generated alternately with the clock .PHI.a at a predetermined interval. By conduction of these analog switches 12 and 14, a signal path from the ground to the integrator 3 through the capacitor 10 and the analog switch 14 is formed. By supplying an input signal through this signal path, an electric charge held in the capacitor 10 is supplied to the integrator 3.
Since the clocks .PHI.a and .PHI.b are alternately generated at a predetermined interval respectively, the operation for holding an electric charge corresponding to the level of an input signal in the capacitor 10 and the operation for supplying this electric charge to the integrator 3 are alternately performed at the predetermined interval and electric current corresponding to the level of the input signal is supplied to the integrator 3. The same operations are performed in the other switched capacitor circuit 2. As a result of performing of the function of a resistance element by these switched capacitor circuits 1 and 2, the circuit shown in FIG. 14 performs a function which is equivalent to an analog filter in which the switched capacitor circuits 1 and 2 are replaced by resistance elements.
In the audio-visual devices which processes analog signals, there are many cases where the filter processing is applied to analog signals of plural channels such as an L-channel and a R channel. In conventional audio-visual devices, filters of a number corresponding to the number of channels are used to cope with such case resulting in a high manufacturing cost of the audio-visual device.